The invention relates to reclosable bags and to methods and apparatus for the manufacture of such bags and more particularly to continuous formation of bags by a form fill and seal process with improved means for advancing the film to intermittently cross-seal and fill the bags.
Reclosable bags having male and female profile cooperating reclosable elements along the opening to the bag have been known for some considerable time. Various forms of manufacture have been employed with one method of making such a bag including extruding a tube where the reclosable elements are integral therewith and the bags are formed by flattening the tube to close the reclosable elements and to cross-seal the flattened tube transversely.
One method of forming bags has been known as the form fill and seal method wherein a continuous length of film is fed forwardly and downwardly over a forming tube with the edges of the sheet of film being sealed to each other. The thus formed tube is cross-sealed at intervals and contents are filled into the bags down through the tubular mandrel over which the bag tube is formed.
An improved form of bag made by the foregoing methods resulted from advancements in the development of reclosable fasteners. Thus, a bag formed in this manner can be openable and reclosable when film which is utilized has a reclosable continuous fastener extending therealong.
In the formation of such bags, it is necessary to intermittently advance the film over the mandrel. Between the intermittent advancement of film, the reclosable fastener (zipper) is ultrasonically spot welded to maintain engagement of the male and female profiles and provide a flattened section for cross-seals to prevent leakage. A cross-seal is formed and contents are dropped gravitationally down through the mandrel to fill the tubular bag. A bag is then advanced and another cross-seal formed to provide the top seal of the previous bag and the bottom seal of a succeeding bag.
The mechanism and method used for the advancement of the film is critical to form the bags of the proper width and it may be even more critical where printing on the bag must be kept in registry. It is also important that the film be advanced without rotating it on the mandrel so that the reclosable fastener will always remain at the right location on the side or top of the bag. Also, the bag must be advanced such that the sealing apparatus will always engage the edges of the bag to form a satisfactory seal between the film edges.
It is accordingly an object of the present invention to provide an improved structure and method for advancement of the film in a form fill and seal apparatus wherein film with a reclosable fastener is used. Another object of the invention is to provide an improved apparatus for advancement of the film in a form fill and seal mechanism wherein relatively delicate film can be handled, and can be accurately and reliably advanced so that the functions of forming the cross-seal, the filling and forming the longitudinal seal can be carried out accurately and reliably.
A further object of the invention is to provide an improved film advancing mechanism which is capable of advancing the film without wrinkling or stressing and wherein accurate control of the increment of advance can be effected.